1. Field of the Invention
The present invention relates generally to gas lift systems for raising liquids in a well to the earth's surface and, more particularly, but not by way of limitation, to gas lift systems for oil wells.
2. Brief Description of the Prior Art
The operation of a gas lift pumping system has been generally described in my U.S. Pat. No. 2,893,493, issued July 7, 1959. As described in that patent, a gas lift system comprises a tubing which extends into a well for receiving liquids in the well and delivering them to the surface. The tubing is enclosed in a casing so that pressurized gas can be introduced into the annulus between the tubing and casing to provide the motive force for driving the liquids to the earth's surface. In order to prevent the pressurized gas from escaping through the tubing, a piston, generally known as a "traveling rabbit," is mounted in the tubing so that the introduction of pressurized gas into the well causes the piston to rise in the tubing to deliver any liquids above the piston to an outlet conduit that is in fluid communication with the tubing. The piston is provided with a valve mechanism that opens when the piston is dropped down the tubing and closes when pressurized gas is introduced into the well. A plunger near the upper end of the tubing catches the piston so that liquid can be permitted to accumulate in the tubing between operations of the system.
The operation of such a system begins with the actuation of the plunger to permit the piston to fall to a stop located near the lower end of the tubing so as to be immersed in the accumulated liquid. Since the valve mechanism is open during this fall, the piston will enter the accumulated liquid with such liquid passing inwardly through the piston during the passage of the piston through the liquid. When the pressurized gas is subsequently introduced into the well, the pressure exerted on the piston causes the valve mechanism therein to close and then forces the piston, and the liquid in the tubing above the piston, up the tubing to the outlet conduit from which the liquid is delivered from the well.
While a gas lift system of this type has many advantages, it also has drawbacks, the major one of which is the need in the prior art systems for a human attendant to operate the system. That is, the attendant actuates the plunger and subsequently introduces the pressurized gas into the annulus between the casing and the tubing. Additionally, the use of pressurized gas as the motive force for raising the liquids requires that the well be provided with a compressor which is both expensive and costly to operate. The present invention provides an improved gas lift system that eliminates these and other disadvantages of the prior art systems.